The Gotthard Base Tunnel is a railway tunnel through the Alps in Switzerland. It opened in June 2016 and full service began the following December. With a route length of 57.09 km (35.5 mi), it is the world's longest railway and deepest traffic tunnel and the first flat, low-level route through the Alps. It lies at the heart of the Gotthard axis and constitutes the third tunnel connecting the cantons of Uri and Ticino, after the Gotthard Tunnel and the Gotthard Road Tunnel.

The Gotthard Pass or St. Gotthard Pass at 2,106 m (6,909 ft) is a mountain pass in the Alps traversing the Saint-Gotthard Massif and connecting northern Switzerland with southern Switzerland. The pass lies between Airolo in the Italian-speaking canton of Ticino, and Andermatt in the German-speaking canton of Uri, and connects further Bellinzona and Lugano to Lucerne, Basel, and Zürich. The Gotthard Pass lies at the heart of the Gotthard, a major transport axis of Europe, and it is crossed by three traffic tunnels, each being the world's longest at the time of their construction: the Gotthard Rail Tunnel (1882), the Gotthard Road Tunnel (1980) and the Gotthard Base Tunnel (2016). With the Lötschberg to the west, the Gotthard is one of the two main north-south routes through the Swiss Alps.